A liquid crystal display which is used as an optical display device is of an indirect light emission type which shows an image by adjusting transmittance of an external light source, and includes a backlight unit as a light source element which is an important part that determines the characteristics of the liquid crystal display.
A backlight unit (which hereinafter may be abbreviated to “BLU”) allows light emitted using a light source such as a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) to sequentially pass through a light guide plate or a diffusion plate, a diffusion sheet, and a prism sheet to reach a liquid crystal panel.
As such, the light guide plate is employed in an edge type backlight unit in which a light source is emitted from the side, among two types which are classified depending on the position of the light source in the BLU used as the light emitting element of a liquid crystal display (LCD).
As illustrated in FIG. 1, the edge type backlight unit is configured such that a light source 20 and a light guide plate 10 are spaced apart from each other by a predetermined gap, but is problematic because when light enters the light guide plate from the light source, some of the light leaks out of the light guide plate, undesirably reducing the quantity of light.
In order to solve this problem, a liquid source-light guide plate structure has been developed, in which a groove is formed on the lateral surface of the light guide plate so that the light source is fitted into the groove. Although such a structure may reduce loss of light of a light incidence unit, there occurs comparative light loss due to the absorption of light by the light guide plate itself.